In electrical power transmission networks accidental contact with high voltage will usually result in severe injury or even death. High security requirements are therefore stipulated throughout such networks.
DC circuit breakers are one security measure conventionally used for, among other things, connecting and disconnecting DC voltage storages connected to a voltage source converter. Such voltage sources comprise battery units designed so that included battery isolation is able to handle a certain breakdown voltage. However, insulation breakdown may still occur resulting in high fault currents between battery cells and battery chassis (cabinet) under voltage application.
A DC voltage storage suitable for use with a voltage source converter handling high voltages often need to comprise several battery units connected in series and forming a battery string, e.g. in transmission and distribution systems the total battery voltage can be in the order of several 10 kV's. The battery string of such DC voltage source will be on high potential even when DC breakers of the DC busbar are opened. Obviously, such high voltage and large amount of energy in the battery string makes it very dangerous for service and maintenance work of the batteries even when they are disconnected from the voltage source converter.
The improvement of the security in high-voltage networks is a continuing strive and in view of this it would be desirable to provide improved security particular in regards of above-described battery storage setups.